This invention relates in general to series-resonating circuits and more particularly to an inductor arrangement with a plurality of integral series-resonating capacitors and which is suitable for use in a subminiature ferrite antenna exhibiting relatively high gain yet being substantially insensitive to hand capacity effects or the like.
In portable radio and paging equipment and related applications, size is of course an extremely important factor. At the same time, no degradation and performance can be tolerated to any large extent. This is particularly so with respect to antenna apparatus. High gain response is most desirable and, indeed, critical if the full range capabilities of the radio or paging equipment is to be realized. However, because of size limitations, the associated antenna arrangement cannot take the usual form of high gain antenna configurations conventionally encountered in the mobile communication or television arts.
One way to achieve an effective compromise between gain and size factors is to employ a ferrite rod antenna for such radio apparatus. This is a magnetic antenna structure as contrasted to the usual electric antenna structure. As is known, magnetic antenna devices of this sort are usually in the form of a rod or cylinder of ferrite material on which a spiral conductor is wound. The spiral conductor forms a completely closed loop and the ferrite core serves to concentrate the magnetic lines of flux and thereby induce an appropriate voltage signal in the closed loop configuration.
The conventional ferrite antenna structure nevertheless has a number of disadvantages, particularly at the relatively high frequencies at which the communications or paging receiver apparatus is expected to operate, say in the UHF frequency range, where problems in effectively resonating the antenna apparatus may be experienced. Too many turns of conductor on the ferrite core results in an inductance which in turn makes the necessary capacitance for resonance simply impractical. That is, the value of the capacitance becomes inordinately small. Reducing the number of turns to obtain a more practical value of resonating capacitance, however, reduces the level of induced voltage and thus is counter-productive with respect to gain.
Moreover, at the higher frequencies, hand capacity, while of a relatively low value, nevertheless presents an alternate or parallel path of sufficiently low impedance to significantly increase the loss factor with respect to the antenna device as a whole. The term "hand capacity" in this regard is used generally to denote one capacitive effect produced by the close proximity of the antenna device to any part of the human body.
Accordingly, it is an object generally of the present invention to provide an improved subminiature antenna structure suitable for use in paging or portable radio apparatus, which antenna structure effectively overcomes the foregoing method deficiencies.
A more particular object of the present invention is to provide a subminiature ferrite antenna structure suitable for use in paging and portable radio communications apparatus operable in the VHF or UHF frequency ranges and which exhibits improved gain characteristics.
Another object of the present invention it to provide an improved subminiature ferrite antenna device of the foregoing type which is substantially insensitive to hand capacitance effects or other loss factors when placed in close proximity to or worn on the person by a prospective user.
It is to be understood that while the present invention may be applied most advantageously to the application of antenna design, and particularly to the design of ferrite antenna structures, it is not limited thereto and may well find appropriate utilization in a wide variety of applications which will become apparent to those skilled in the art.
Accordingly, it is a further object of the present invention to provide an inductor arrangement with a plurality of integral series resonating capacitors for selective control of the terminal impedance of such inductor device without regard to the level or magnitude of inductance involved.